Previously known working units of the type having a motor and a machining tool carrying output spindle suffer from a rather slow working action. This is due both to the fact that the working unit has a relatively large mass and to the fact that the speed of the motor is relatively low. By nature, a heavy working unit is difficult to move at high velocity either in a plain reciprocating movement or in a more or less complicated working pattern, which means that the working process time will be undesirably long. Also, a relatively slow motor limits the maximum feed speed of the working tool relative to the work piece.
A heavy output spindle unit including a tool chuck also means a large rotating mass, which tends to create vibration problems at high speed rotation. It is difficult to avoid resonance frequencies in such a known device.
One reason why previously known movable working units has a relatively large mass is a rather complex design of the motor and output spindle arrangement.
Another reason why previous working units has a large mass is the use of electric motors with all their heavy iron cores and copper windings. Electric motors also have a limited rotation speed which limits the rotation speed of the working tool, and, thereby, the possible feed speed of the working tool.